Ok let's put things into perspective .... Hitachi don't issue the codes ... Each manufacturer integrates compatibility with a range of brands ... the actual setup belongs to Humax not Hitachi (so they're not refusing ... they just don't know)
The handbook on the web is normally kept up to date .... so almost certainly the info required is here
http://www.humaxdigital.com/uk/pdf/PVR-8000T_8 0G_L.pdf
there is also a getout clause in the book which says that some models may not be supported
Further ... if the TV is a very recent model ....you are possibly out of luck ... unless the remote has the facility to update itself.
(having said that most brands use the same basic signals ... so work through the codes in the book ...
failing that consider something like
http://www.logitech.com/index.cfm/remotes/univ ersal_remotes/&cl=us,en
the 525 is excellent ... and DOES update itself